ZX Printer Instructions
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ZX Printer instructions Copyright Sinclair Research Limited 1981 ZX Printer Operating Instructions Introduction The Sinclair ZX printer gives a permanent record if anything the computer can print on the TV screen. In addition, graphics always "join up" if done in several goes, so that long programs, long tables of results and elaborate patterns and graphs can be printed out without a break. Supplied with a printer are these instruction and 1 reel of paper. You will also need either a ZX81, or a ZX80 with the replacement ROM: the standard version of the ZX80 cannot be used. Chapeter 20 of the ZX81 instruction book gives the BASIC commands necessary to use the printer. You will also need a 1.2A power supply which will have been supplied either with your computer or your printer. Connecting up Before connecting anything to you computer, pull its power plug out. If you have a RAM pack, unplug that too. The edge socket on the end of the printer's cable now pushes onto the back of the computer through the rectangular slot - which is on the left of the ZX80 and on the right of the ZX81 (looking from the front). The printer will work perfectly well without a RAM pack, but if you have one an extra plug has been provided behind the printer's socket so that the two may be stacked together. Just push the RAM into the back of the socket housing the same way as if you were connecting it to the computer. The printer should now sit neatly on the right hand side of the ZX80/81. IMPORTANT:Since the printer takes a lot of power, a new power supply is provided which must be used in place of the old computer suplpy, and which plugs into the same socket on the ZX80 or ZX81. No harm will be done using the replacement supply all the time, even if the printer isn't connected. Note - since you should'nt connect the printer without switching the computer off first, it's a good idea to have the printer always plugged in just in case - otherwise you'll have to save your program to tape while you fiddle about with plugs and sockets. See LPRINT inside back cover The paper The ZX printer uses its own special metallized paper, which can be supplied by Sinclair Research. Other metal-coated papers will work, but may give smeared, fuzzy or faint printing - others contain cadmium in the coating and could be a health risk. Non-metallized paper won't work at all. How to load a fresh reel of paper Press on the underneath of the reel With the reel carrier pulled out of the prtiner, take out the carrier to disengage it from the empty cardboard tube - but save the plastic hubs in the ends printer. Thread the end of the new reel Push the hubs into the reel, and clip it into the carrier underneath the metal roller. Pull some of the paper through, hold the carrier as shown and clip it back into the printer body. This may be done while the printer and computer are switched on, so long as care is taken not to disturb the connections. The feed button This is the printer's only control, situated to the right of the paper reel. This feeds paper out without printing anything to give a blank between printouts or when tearinf off. The feed button doesn't communicate with the computer, so it can be pressed at any time, even when the ZX80 or ZX81 is in the middle of a program. If you press the button whilst the printer is actually printing, however, the computer will be overridden for as long as the button is held down and you'll get a blank - no harm will be done, but the printout during that time will be lost. Tearing off Sections of the paper may be torn off using the printers serrated edge - next to where the paper comes out. Use the feed button to get a manageable length of paper and/or to make sure that the rinting is clear of the serrations. Less thant 2 or 3 inches of paper may be difficult to tear off properly. (If you're right handed). Hold the printer steady with your left hand; with your right, pull the paper across the serrations at a farily steep angle. Don't try to pull the paper squarely across the edge all at once. Practice makes perfect - if you're any in doubt about the above procedure try tearing off a few strips of blank first. Cleaning After you've been through a whole reel, you'll find that some of the black material has been scraped off the paper. Whilst you have the reel carrier out, the printer should be cleaned. The black deposit should be removed from the recess where the reel carrier goes especially around the slot just underneath the serrations, and from the rubber drive roller. Use only tissues or a soft brush - chemicals are definitely out. Some of them will attack the plastic and may reduce your printer to a shapeless black blob... Also, don't poke anything into any of the apertures, as the electronics or mechanics may be damaged, and don't try to take the printer apart. Dismantling is easy, reassembly may be more difficult... ZX printer technical appendix This section is written for people who wish to use their printer with machine code programs to do things like high resolution graph plotting, alternative character sets, etc, and it assumes a knowledge of Z80 hardware and software. For printing out ZX81 characters from a BASIC program you don't need to understand this section at all. General principle of operation The printer functions in rather the same was as a TV, i.e. by scanning from left to right. A conductive stylus is pulled across the paper at high speed, and where a black dot is wanted a pulse of current is passed though the stylus. This evaporates the aluminium coating on the paper, and allows the black backing to show through. To avoid the need to return the stylus quickly to the left hand edge of the paper, there are in fact two styli, mounted on a moving belt, which follow each other in quick succession. The belt and the paper feed roller are both driven continuously whilst printing; so that when the next stylus comes round the paper has been moved up ready for the next line. In order that the styli always stop off the paper, the BASIC commands slow the motor down for the last two scans before stopping - this makes sure that graphicsalways "join up" if done in several goes, and this feature should be put in any machine code program that requires the printer to stop whilst the computer thinks about the next line. At full speed, each pen is on the paper for about 32ms, and off it for about 16ms. Since the speed of printing can vary, an encoder disc is used to give 256 pulses across a 92mm print width (allowing 4mm margins). These pulses are synchronised with the stylus hitting the paper so that the printing is always vertical. There is about 60 s between the starts of successive pulses at full speed. The interface The printer is wired as a Z80 I/O port, selected by A2 being at a low level - no other address oinse are recognised. So to send information to the printer, use the Z80 command OUT (FB),A - opcode D3 FB assuming the data is in register A. The data bits have the following meanings: (D2) High level means stop the motor, low means start it. (D1) High level means put the motor on slow speed - this line is overridden by D2 being high. (D7) High level applies power to the stylus. All these lines remain in the stat they were at last, until new data is sent to the printer. At switch on, or after pressng the feed button, D1 and D7 are set low; D2 is left high once feed is finished. The other data lines aren't used. To fetch information frmo the printer, the Z80 instruction: IN A, (FB) - opcode DB FB; will put the data into the accumulator. These bits are used: (D6) Will be erased as low if the printer is there, high if it isn't, and is used solely to check the printer is connected. (D0) This line is the signal from the encoder disc. (D7) This line is high when the stylus hits the paper D0 and D7 are both latched so that they remain high until the computer writes something to the printer. So even if you don't make use of the information you've read in, you should output instruction (with appropriate data) to reset the latches until the next signal. These bits may be in either state on switch on, and aren't affected by the feed button. The paper detect signal is also used internally by the printer to make sure that the styli stop off the paper. Note that if power is applied to the stylus, the paper signal will go high even if the pritner is between scans, and so the stylus must be turned off before attempting to detect the edge of the paper. Some programs Here are a few example programs for experimenting with. "Text Edit" (No. 1) uses the printer like a typewriter except that it automatically prevents words from being chopped in half by the end of the line.